Structured fluids with a relatively high resistance to flow (yield stress) are highly demanded in the adhesives, gel coats, composites, and coatings markets. One method of modifying the rheological properties of such compositions is to incorporate particles, particularly fumed silica particles, into the composition. Fumed silica has a low bulk density and high surface area, and its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler. When used in a matrix (e.g., polymer, solvent, resin, etc.), the flow properties of the composition are determined by particle-matrix and particle-particle interactions. In order to obtain desirable properties, the particle-particle interactions must be strong enough relative to the particle-matrix interactions to form a network of particles in the composition. If the particle-particle interactions are weaker or smaller in number than the particle-matrix interactions, the system will act as a suspension and a network will not be formed. Thus, in polar systems, highly hydrophobic particles have been used as rheological control agents. However, highly hydrophobic particles can be difficult to disperse in a polar matrix, and may tend to remain agglomerated as they were in the powder form, thereby reducing the number of contact points that are necessary to create a strong network. This not only creates difficulties in processing, but also may result in sub-optimal initial or retained yield-stress properties. Thus, there is a need for treated silica particles that can provide improved rheological performance.
Electrophotographic image formation comprises developing an electrostatic latent image formed on a photoreceptor with a toner comprising a colorant dispersed in a binder resin, transferring the toner image to a receiving paper, and fixing the transferred toner image by means of, for example, a hot roll. The photoreceptor is cleaned after the transferring step to prepare for the next latent image formation.
Silica particles are often combined with toner particles to improve one or more selected properties of the toner particles, including fluidity, transferability, fixability, and cleaning properties. Typically, the silica particles are subjected to a chemical treatment to render the surface of the particles hydrophobic. However, there is a continued need for developing treated silicas to provide desired properties applicable for toner compositions.